In the construction industry and other fields of heavy engineering such as mining, percussion power tools are widely used, for example to break up hard surfaces, compact loose material such as back-fill, and drive posts or piles into the ground. The tools incorporate a reciprocating mass, usually driven by compressed air but also by other means, which repeatedly impacts against a load-bearing surface within the tool. The movement of the mass towards the surface is known as the power stroke, whilst the reverse movement is known as the return stroke. It is known, for example in so-called hammer action drills, to incorporate a ratchet mechanism to rotate the tool during the return stroke.
The total work output of percussion power tools is dependent on the extent to which the reaction force between the tool and the work piece is able to counteract the force acting on the reciprocating mass during the power stroke. With hand-held systems acting on the ground, the reaction force is given by the sum of the deadweight of the tool and any downward pressure applied by the operator. The maximum deadweight for conventional heavy-duty paving breakers is approximately 40 kgs, otherwise the tool becomes too heavy to lift. The maximum deadweight for conventional heavy-duty rock drills is around 25 kgs; such drills tend to be held by the operator in a much higher position compared with paving breakers and therefore, for ergonomic reasons, they must be lighter.
There is a trend with hand-held percussion power tools to minimise the contribution of the operator to the reaction force in order to increase operator comfort and reduce the risk of contracting hand/arm vibration syndrome, HAVS.